1. Field of the Invention
This invention relates to a process for recovering carotene from a native fat or oil, more particularly from palm oil.
Depending on its origin, crude palm oil contains between 500 and 3,000 ppm of carotinoids containing a high proportion of beta-carotene and relatively low concentrations of tocopherols, tocotrienols and sterols.
Among the carotinoids, there are the oxygen-containing derivatives (xanthophylls) and the carotenes. The most well-known carotenes are alpha-, beta- and gamma-carotene and also lycopene. Beta-carotene occurs predominantly in nature and is the actual provitamin A. Since the carotenes are natural compounds and since they all show pronounced provitamin A activity, they are widely used as antioxidants or as dyes in commercial applications in the pharmaceutical industry, in the food industry and in the manufacture of cosmetics. More recently, the tumor-inhibiting activity of beta-carotene has been repeatedly demonstrated so that it is now also used in the prophylaxis of cancer.
2. Discussion of the Related Art
Several different processes for recovering carotene from palm oil or at least for concentrating carotene are known from the prior art.
In some known processes, the palm oil is first transesterified and/or saponified and then concentrated by extraction or distillation. Thus, according to U.S. Pat. No. 2,460,796, the palm oil is first transesterified with methanol. After the reaction mixture has settled out, the upper phase consisting of fatty acid methyl ester with dissolved carotene is washed with a mixture of alcohol and water and then with water alone. The complete or partial removal of the fatty acid methyl ester, which may be used for the production of soap, by distillation leaves a carotene concentrate. The distillation step is carried out in vacuo at temperatures of up to 150.degree. C. The total distillation time mentioned in this document is around 5 hours.
The disadvantage of this known process lies in the high temperatures to which the heat-sensitive carotene is exposed and which rule out a high yield of carotene.
In another process known from U.S. Pat. No. 2,572,467, palm oil is first saponified (Examples I and II). Dilute sulfuric acid is added to the reaction mixture to obtain the corresponding free fatty acids. After settling, the fatty acid phase is dissolved in acetone and filtered. The filtrate is repeatedly cooled and refiltered to obtain a residue consisting of fatty acids and a carotene-containing solution from which carotene can be crystallized out at -70.degree. C.
In a variant of this known process, transesterification with methanol replaces saponification of the palm oil with subsequent acid treatment (Examples III and IV of the same U.S. patent).
In a process described in U.S. Pat. No. 2,652,433, palm oil is subjected both to transesterification and to saponification. After neutralization and filtration, the crude palm oil is transesterified with methanol. Saponification of the ester phase is followed by an extraction step with petroleum ether or chloroform. The residue obtained after removal of the petroleum ether by distillation contains around 3% of carotene.
U.S. Pat. No. 5,157,132, which was published in 1992, discloses a process for concentrating carotene from palm oil which also begins with a transesterification step. The ester-rich phase obtained after settling is extracted with methanol and water to obtain a phase rich in carotene. Repeated extraction with methanol leaves a concentrated methanol/carotene mixture from which the alcohol is removed by evaporation in vacuo (Example I). In addition, the carotene-containing fatty acid methyl ester can be saponified after the transesterification step before it is extracted with petroleum ether. In this process, therefore, all the carotene-containing fatty acid methyl ester is saponified (Example II).
According to GB 2,218,989 A, the crude palm oil is subjected after transesterification with methanol to liquid chromatography with methanol and a mixture of hexane and methanol or chloroform as mobile solvent to obtain a fraction rich in carotene.
The disadvantage of extracting carotene from fatty acid methyl ester is that the fatty acid methyl ester is contaminated with the extractant which prevents the ester from being further processed by hydrogenation to fatty alcohol. In general, the ester obtained in this process cannot be put to any further use and has to be disposed of. The same disadvantage attends the extraction processes which start directly from palm oil without preliminary transesterification.
A process without this disadvantage is described in U.S. Pat. No. 2,432,021 where carotene is obtained in concentrated form by extraction with liquefied propane and subsequent rectification. Although, in this case, the palm oil can be subsequently used for the production of fatty alcohol, the process cannot be carried out economically on an industrial scale.
In addition, adsorptive processes for concentrating carotene are known from GB 691, 924, from GB 1,562,794 and from U.S. Pat. No. 2,484,040.
To summarize the prior art, it may be said that the known processes either cannot be economically carried out on an industrial scale or the yield of carotene is too low as a result of thermal and/or chemical decomposition or poor selectivity or that, after the process has been carried out the palm oil or the palm oil derivative is no longer suitable for the production of fatty alcohols.